Topband: Skin effect on RG6U at top band

[ZR]

CATV requirements start at 5MHz so I have my doubts that the cable is at 
fault. Ive heard a similar complaint from Australia with copper braid RG-6 
so wonder if it is a non USA product problem. Maybe the Chinese are saving 
copper!

About 20 years ago I ran 750' of CATV quad shield RG6 which is aluminum 
braid and shield to a relay box. It worked very well only to be destroyed by 
critters in a month or so. Replaced it with obsolete .412" CATV hardline and 
dont remember any difference; the .412 is still in use.

Prior to that at another QTH I had about 1200' of RG-6 running thru branches 
and that heard well also and was used up to 20M (with a preamp) when snow 
static wiped out yagi reception.

With the new Beverage system Im using up to 250' runs of RG6 quad shield and 
flooded to relay boxes but its all elevated about 5' except where it has to 
cross areas that I need to get a vehicle thru. With proper grounding and 
common mode chokes there is absolutely no pickup.

Carl
KM1H



----- Original Message ----- 
From: "jeremy maris" <jeremy at maris.plus.com>
To: <topband at contesting.com>
Sent: Monday, January 31, 2011 5:19 AM
Subject: Topband: Skin effect on RG6U at top band


> We've used 1 km of coax to feed a remote Beverage (3 wavelength, 60
> degrees, for VK and far east). 750m of the coax is RG6U, with copper
> braid. The results were poor, despite a 10dB head amplifier at the end
> of the Beverage, so we measured the coax attenuation on part of the
> run by putting 25W into the coax and measuring power into a 50 ohm
> power meter. I appreciate this isn't 75 ohm like the coax but extra
> losses from 1.5:1 SWR should be low.
>
> The measured loss in the first 250m segment was ~ 6dB and about ~9dB
> in the second segment, 15dB total over 500m. This is way higher than
> published figures (eg at 
> http://www.timesmicrowave.com/cgi-bin/calculate.pl)
>   which suggest about 3dB per 250m.
>
> I'm thinking that the copper plating on the RG6/U inner conductor is
> too thin. N6LF gives the skin depth at 2MHz as 40uM (Conductors for HF
> Antennas, Rudy Severns, QEX November/December 2000). Does anyone have
> any typical figures for the plating thickness of RG6/U or have
> evidence that attenuation figures at 2MHz are much higher than expected?
>
> 73
>
> Jeremy G3XDK
>
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